INTERFACE MICROMOTION FAILURE SIMULATION
OF CEMENTLESS HIP PROSTHESIS
(SIMULASI KEGAGALAN PERGERAKAN MIKRO
ANTARAMUKA IMPLAN TULANG PINGGUL
MENGGUNAKAN KAEDAH TANPA SIMEN)
MOHAMMED RAFIQ BIN DATO’ ABDUL KADIR
RESEARCH VOTE NO:
78057
PUSAT PENGURUSAN PENYELIDIKAN
UNIVERSITI TENOLOGI MALAYSIA
2007
INTERFACE MICROMOTION FAILURE SIMULATION
OF CEMENTLESS HIP PROSTHESIS
(SIMULASI KEGAGALAN PERGERAKAN MIKRO
ANTARAMUKA IMPLAN TULANG PINGGUL
MENGGUNAKAN KAEDAH TANPA SIMEN)
MOHAMMED RAFIQ BIN DATO’ ABDUL KADIR
RESEARCH VOTE NO:
78057
Jabatan Kejuruteraan Bahan
Fakulti Kejuruteraan Mekanikal
Universiti Teknologi Malaysia
2007
Acknowledgements
I would like to acknowledge the Ministry of Higher Education for providing the research
grant of RM15,000. Thank you also to all staff at the Research Management Centre,
UTM, for providing all the support so that the research can be completed successfully.
Lampiran 20
UTM/RMC/F/0024 (1998)
UNIVERSITI TEKNOLOGI MALAYSIA
BORANG PENGESAHAN
LAPORAN AKHIR PENYELIDIKAN
TAJUK PROJEK :
Saya
Interface Micromotion Failure Simulation of Cementless Hip Prosthesis
MOHAMMED RAFIQ BIN DATO’ ABDUL KADIR
(HURUF BESAR)
Mengaku membenarkan Laporan Akhir Penyelidikan ini disimpan di Perpustakaan
Teknologi Malaysia dengan syarat-syarat kegunaan seperti berikut :
Universiti
1.
Laporan Akhir Penyelidikan ini adalah hakmilik Universiti Teknologi Malaysia.
2.
Perpustakaan Universiti Teknologi Malaysia dibenarkan membuat salinan untuk
tujuan rujukan sahaja.
3.
Perpustakaan
dibenarkan
membuat
penjualan
Penyelidikan ini bagi kategori TIDAK TERHAD.
4.
* Sila tandakan ( / )
salinan
Laporan
Akhir
SULIT
(Mengandungi maklumat yang berdarjah keselamatan atau
Kepentingan Malaysia seperti yang termaktub di dalam
AKTA RAHSIA RASMI 1972).
TERHAD
(Mengandungi maklumat TERHAD yang telah ditentukan oleh
Organisasi/badan di mana penyelidikan dijalankan).
TIDAK
TERHAD
TANDATANGAN KETUA PENYELIDIK
Mohammed Rafiq bin Dato’ Abdul Kadir
Ketua Projek 78057
Tarikh : 31 Disember 2007
CATATAN :
* Jika Laporan Akhir Penyelidikan ini SULIT atau TERHAD, sila lampirkan surat daripada pihak
berkuasa/organisasi berkenaan dengan menyatakan sekali sebab dan tempoh laporan ini perlu dikelaskan sebagai SULIT dan TERHAD.
Lampiran 13
UTM/RMC/F/0014 (1998)
UNIVERSITI TEKNOLOGI MALAYSIA
Research Management Centre
PRELIMINARY IP SCREENING & TECHNOLOGY ASSESSMENT FORM
(To be completed by Project Leader submission of Final Report to RMC or whenever IP protection arrangement is required)
1.
PROJECT TITLE IDENTIFICATION :
INTERFACE MICROMOTION FAILURE SIMULATION OF CEMENTLESS HIP PROSTHESISng
Learning Styles: Their Impact On University Student's Learning
Orientations Study Skills
and Academic Achievements
2.
Vote No:
780571
PROJECT LEADER :
Name : MOHAMMED RAFIQ BIN ABDUL KADIR
Address
: DEPARTMENT OF MATERIALS ENGINEERING,
FACULTY OF MECHANICAL ENGINEERING,
UNIVERSITI TEKNOLOGI MALAYSIA.
Tel
3.
: 07-5534806
Fax : 07-5566159
e-mail : rafiq@fkm.utm.my
DIRECT OUTPUT OF PROJECT (Please tick where applicable)
Scientific Research
Applied Research
Algorithm
Structure
Product/Process Development
Method/Technique
Product / Component
Demonstration /
Process
Prototype
Data
Other, please specify
4.
Software
Other, please specify
Other, please specify
___________________
__________________
___________________________
___________________
__________________
___________________________
___________________
__________________
___________________________
INTELLECTUAL PROPERTY (Please tick where applicable)
Not patentable
Technology protected by patents
Patent search required
Patent pending
Patent search completed and clean
Monograph available
Invention remains confidential
Inventor technology champion
No publications pending
Inventor team player
No prior claims to the technology
1
Industrial partner identified
UTM/RMC/F/0014 (1998)
5.
LIST OF EQUIPMENT BOUGHT USING THIS VOT
COMPUTER
PRINTER
EXTERNAL BACKUP HARD DRIVE
6.
7.
STATEMENT OF ACCOUNT
a)
APPROVED FUNDING
RM : 15,000.00
b)
TOTAL SPENDING
RM : 14,999.55
c)
BALANCE
RM : 0.45
TECHNICAL DESCRIPTION AND PERSPECTIVE
Please tick an executive summary of the new technology product, process, etc., describing how it
works. Include brief analysis that compares it with competitive technology and signals the one
that it may replace. Identify potential technology user group and the strategic means for
exploitation.
a)
Technology Description
The project involves the establishment of techniques to simulate failure after femoral
replacement. The following steps have been recognized as one of the methods for
simulation: Reconstruction of human joint either from CT dataset or from three dimension
bone banks, design of a suitable hip prosthesis to fit the bone model, virtual reaming of
the bone to represent bone bed preparation, and finally analyzing failure using finite
element.
b)
Market Potential
This technique can be widely used in the design and development of new hip prosthesis.
With the increase of imported orthopaedic products nationwide, the technique can be
used by local implant manufacturer to develop a locally made femoral prosthesis.
2
UTM/RMC/F/0014 (1998)
c)
Commercialisation Strategies
This project has already established a method to analyse failure of hip replacement. This
method can be used by implant manufacturers for their newly developed hip stem.
However, the technique should already be well established for international implant
manufacturers. The best way to proceed is to do consultation services to local
manufacturers, and at the same time develop the tools into a standalone software for
commercialization.
8.
Signature of Projet Leader :-
Date :-
______________________
__________________
RESEARCH PERFORMANCE EVALUATION
a)
FACULTY RESEARCH COORDINATOR
Research Status
Spending
Overall Status
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
( )
Excellent Very Good Good Satisfactory
( )
( )
( )
Fair
Weak
Comment/Recommendations :
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
…………………………………………
Signature and stamp of
JKPP Chairman
Name : ………………………………………
Date
3
: ………………………………………
UTM/RMC/F/0014 (1998)
RE b)
RMC EVALUATION
Research Status
Spending
Overall Status
( )
( )
( )
( )
( )
( )
( )
( )
( )
Excellent Very Good Good
( )
( )
( )
( )
( )
( )
( )
( )
( )
Satisfactory Fair
Weak
Comments :_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
_____________________________________________________________________________
Recommendations :
Needs further research
Patent application recommended
Market without patent
No tangible product. Report to be filed as reference
………………………………………..
Name : ……………………………………………
Signature and Stamp of Dean /
Deputy Dean
Research Management Centre
Date : ……………………………………………
4
ABSTRACT
The most commonly reported failure modes of cementless hip stems are loosening and thigh pain; both are
attributed to the relative motion at the bone-implant interface due to failure to achieve sufficient primary
fixation. Accurate predictions of hip stems’ stability are therefore crucial to the pre-clinical analyses of
hip arthroplasty. This study uses finite element technique to analyse the effect of muscle forces on the
predicted micromotion and therefore stability of cementless femoral components. An in-house
experimentally validated micromotion algorithm was used in analyses simulating two of the most common
physiological activities – walking and stair-climbing. The results showed that models where muscle loads
were included had ten times larger micromotion than those modelled without muscle loads. Ignoring
muscle forces in any pre-clinical evaluation of femoral stems are therefore not advisable as it will
overestimate the stability of the stem.
Keywords: Hip arthroplasty, Cementless stem, Finite element, Muscle loadings, Primary stability,
Interface micromotion.
ABSTRAK
Mod kegagalan yang selalu dilaporkan apabila pembedahan tulang tanpa menggunakan simen adalah
kelonggaran dan sakit peha; kedua-duanya disebabkan gerakan antara implan relatif kepada tulang
disebabkan kegagalan untuk mencapai ikatan pertama yang kuat. Ramalan yang tepat terhadap kestabilan
implan tulang peha adalah amat penting dalam menganalisa sebelum pembedahan dibuat. Kajian ini
menggunakan kaedah unsure terhingga untuk menganalisa kesan beban otot terhadap ramalan gerakan
mikro dan sekaligus menentukan kestabilan implan tanpa menggunakan kaedah simen. Satu algoritma
gerakan mikro yang telah divalidasi secara eksperimen telah digunakan di dalam analisa dua gerakan
fisiologi – berjalan dan menaiki tangga. Keputusan menunjukkan simulasi dimana beban otot dimasukkan
mempunyai 10 kali ganda gerakan mikro daripada simulasi dimana beban otot tidak dimasukkan. Semua
analisis untuk mengenalpasti gerakan mikro dengan itu mestilah memasukkan beban otot untuk
memberikan ramalan yang tepat.
Kata Kunci: Pembedahan tulang peha, Implant tulang peha tanpa simen, Kaedah unsure terhingga,
Beban otot, Kestabilan pertama, Gerakan mikro antaramuka..
Chapter 1
Introduction and Literature
Review
The number of people undergoing hip joint replacement surgery has increased over
the past decades. In the UK alone, more than 60,000 total hip arthroplasties (THA)
are performed annually, 15% of which are performed in the younger age group (less
than 57 years old) (Tennent & Goddard 2000). Most hip replacements are performed
on patients suffering from osteoarthritis, a joint disease associated with the wearing
away of the cartilage covering the bone ends. Other degenerative hip disorders that
could require THA include rheumatoid arthritis and avascular necrosis. The primary
aim of the replacement surgery is to relieve pain and regain mobility. Pioneered in
1962 by the renowned English surgeon, Sir John Charnley, the development of
orthopaedic implants used in hip arthroplasty has improved steadily, making it one of
the most successful surgical procedures. However, with the increase in the number of
hip replacements performed, the scope and frequency of complications appear to be
increasing. Complications such as stress-shielding, osteolysis and aseptic loosening
remain some of the major problems in hip arthroplasty (Macdonald 1998).
There are mainly two types of hip arthroplasty in use today – cemented and
cementless. Hip prostheses with the use of cement are the most commonly used but
1
the cementless techniques are gaining popularity.
Fixation of these femoral
components is a major concern because bone growth could only be achieved on stable
implants (Pilliar 1991; Simmons, Valiquette & Pilliar 1999). Failure to achieve a
strong fixation will result in the formation of fibrous tissue layer at the bone-implant
interface and the eventual loosening of the implant (Pilliar, Lee & Maniatopoulos
1986). PMMA is used in the cemented type prostheses to provide strong primary
fixation. However, cement debris can cause complications such as inflammation and
bone lysis. One of the solutions to this problem is to abolish the use of cement, thus
the cementless femoral component. However, without the cement these implants
could not achieve initial fixation, unless the design is modified so that proper and
adequate stability could be achieved. The design of femoral prostheses, together with
the surgical techniques of implantation, continues to receive much attention in the hip
biomechanics community.
Degenerative hip disorders are the major reason for hip joint arthroplasty.
The
disease can become so severe that replacement surgery is the only way to remove pain
and regain mobility. In this section several major hip disorders are discussed, as well
as a brief introduction to a common skeletal disorder of osteoporosis.
Osteoarthritis is a degenerative condition associated with the wearing away of the
cartilage covering the bone-ends. Cartilage is used to absorb the stresses put on a
joint, and protects the bones from damage. Osteoarthritis occurs when the cartilage
deteriorates, either due to age or injury. With age, human joints slowly lose the
ability to regenerate and repair the cartilage. Bone growths develop as the cartilage
degenerates, and the bones that make up the joint rub together, causing pain and
restriction of movement. It is a progressive disease that can affect any or all of the
joints in the human body, with the weight-bearing joints such as the hips and the
knees being more susceptible than the others.
Currently, no cure exists for
osteoarthritis. Treatment options centre on prevention, if possible, and control of the
disease. At its worst, the disease can cause constant pain and severely reduced
mobility.
Rheumatoid arthritis is another form of arthritis that is chronic and affects many
different joints.
It begins with an inflammation and thickening of the synovial
2
membrane, which causes pain and swelling, followed by bone and cartilage
degeneration and disfigurement. The disease is considered to be an autoimmune
condition that is acquired, and in which genetic factors appear to play a role. It
appears more frequently in older people, with more women being affected than men.
Avascular Necrosis (AVN) is a skeletal disease that occurs when bone tissues die off,
resulting in the collapse of the bone. It is caused by the loss of blood to the bone.
Hips are one of the areas most commonly affected by the disease. Common names
for this disease include osteonecrosis, aseptic necrosis and ischemic bone necrosis.
The disease can be caused by excessive use of drugs and alcohol or by injury. A joint
that has been injured through fracture or dislocation has an increase risk of AVN
because blood vessels may be damaged, and blood circulation to the bone is disrupted
resulting in trauma-related AVN. Arthritis and AVN affect both men and women at
higher rates as they age. The majority of cases involve people between the ages of 30
and 50 years. However, it can affect people of all ages.
Osteoporosis is a major skeletal disorder in which nutrition plays a role and can be
prevented and treated. It is characterised by a significant loss of cancellous bone
stock and structural deterioration of bone tissue, causing it to become fragile and more
likely to fracture. If left untreated, the disease can progress without symptoms until
the bones became so weak that a sudden strain, bump, or fall causes a fracture.
Fractures occur typically in the hip, spine and wrist. Women are more likely to suffer
from osteoporosis than men. Osteoporosis is not a cause for joint replacement, but if
a replacement is required due to fracture for example, then it affects the decision
made by the surgeon because of the structural deterioration of the bone.
There are two major types of artificial hip replacements: cemented and uncemented.
Both are widely used. The superiority of one compared to the other remains a topic of
debate. The choice made by orthopaedic surgeons is usually based on the patient’s
age, type of disease, anatomy, lifestyle, and the surgeon's experience. The surgeon's
criteria of a suitable hip implant include:
Shape and design for optimum fit within the patient's anatomy.
Shape and design which allow for optimum surgical technique.
3
The implant’s clinical history of stability – called fixation.
The exterior coating of the stem, which contributes to optimum fixation.
The type of surgery – primary, revision or fracture.
Cemented prostheses are the oldest form of hip arthroplasty. They are held in place
by a type of epoxy cement that attaches the stem to the bone. Good clinical results at
10 years are achievable through this method (Emery et al. 1997). There are, however,
complications arising from this conventional method of fixing artificial joints, mainly
from the use of the cement itself. PMMA degrades over time and the built-up of
cement debris causes inflammation of the surrounding bone and loosening at the
interface (El-Warrak et al. 2001).
Revision surgery, if required, will also be a
problem due to the significant removal of bulk cancellous bone during the first
surgery.
Despite these complications cemented techniques are still widely used
depending on the condition of the patients. It has been suggested for use in the older
patients above 65 years (Dorr, Wan & Gruen 1997), or on patients with osteoporotic
bone condition or poor bone stock to ensure strong primary fixation (Haber &
Goodman 1998). However, Harris (1997) strongly believed that cemented techniques
not only worked well with the elderly, but also for younger patients.
Early total hip arthroplasty using the cementing technique in the late 1960s and early
1970s showed an incidence of femoral component loosening of 30%-40% at 10 years
(Stauffer 1982; Sutherland et al. 1982). These disappointing results led to revised
cementing techniques (Rasquinha et al. 2003), and the use of bioactive cement to
encourage rapid bone ingrowth (Oonishi 1991). Some authors also suggested limiting
the cement to the proximal area only (sometimes called the hybrid option) (Monti,
Cristofolini & Viceconti 2001).
The cementless alternative is used to eliminate the problems associated with the use
of cement. The diameter of the stem is generally larger than its cemented counterpart
in order to fill the canal, and the surface is usually roughened with particles through
grit-blasting or plasma-spraying.
Roughened surfaces are not recommended in
cemented stems; they are usually polished in order to reduce cement wear debris
(Duffy et al. 2001).
Some cementless designs also have macro-features at the
proximal part such as a porous coating or fibre meshing. These features are beneficial
4
in cementless implants because they provide a medium for biological attachment that
secures the implant onto its place.
The roughened surface encourages bone
attachment and the macro-features allow new bone to attach and grow into, creating a
strong bond between the patient’s own natural tissue and the implant (Whiteside et al.
1993).
Besides the promising results of cementless stems, old complications associated with
the cemented technique are still not entirely eliminated.
Stress-shielding, for
example, still occurs in hip replaced with cementless stems (Nourbash & Paprosky
1998). Osteolysis also occurs in cementless arthroplasty due to wear debris. It was
previously thought that migration of cement debris along the bone-cement interface
was the cause of osteolysis, due to the detection of particles of PMMA of various
sizes found in failed interface membranes. However, a study by Boss et al. (1990)
showed that the release and deposition of wear products, of whatever nature, were
apparently responsible for osteolysis.
Aseptic loosening is a major concern in cementless hip stems, and it is a failure
associated with the lack of stability. It can be divided into 2 categories (Horikoshi et
al. 1994). The 1st category is a late failure due to osteolysis which can be explained
by excessive wear particles that migrate along the implant-bone interface and result in
formation of the activated interfacial membranes. Early failure, on the other hand,
can be explained by the lack of initial implant stability or catastrophic failure of metal
or polyethylene materials. Aseptic loosening is still a major problem in cementless
design. This could be seen in a recent follow-up report of a carbon fibre-reinforced
composite stems, where 92% of the stems were revised due to aseptic loosening at 6
years (Adam et al. 2002). The authors blamed the high rate of loosening on deficient
primary stability due to the bad design.
Finite element models of joint anatomy can help surgeons understand trauma from
repetitive stress, degenerative diseases such as osteoarthritis, and acute injuries. FE
models of prosthetic joint implants can provide surgeons and biomechanical engineers
with the analytical tools to improve the life-span of implants and improve the clinical
outcomes of total hip replacement surgeries (O’Toole et al. 1995). These models are
created from many small “elements” of triangular or rectangular shapes. When these
5
finite element (FE) models are loaded with proper boundary conditions, their
responses are obtained by solving a set of simultaneous equations that represent the
behaviour of the model under load.
FE analyses have been widely used in the study of hip joint arthroplasty and in
particular the study of hip stem stability.
FEA is used to complement the
experimental work on micromotion and could even become a useful tool to assess the
suitability of implants before surgery (Huiskes et al. 1998; McNamara et al. 1997).
One advantage of using FE methods in analysing the stability of hip stems is that it is
a non-destructive assessment that can measure the distribution of micromotion along
the entire surface of the stem. In-vitro experiments, on the other hand, could only
measure micromotion at certain points, and the drilling of holes during specimen
preparation could damage and weaken the surrounding bone, thus overestimating the
relative motion. FE analysis gives a clearer picture of the stem being analysed and
could pointed out ways of improving the stability further. Finite elements have been
shown to predict experimental findings and long-term failure mechanisms in
orthopaedic surgery with excellent accuracy (Stolk et al. 2003; Tanner et al. 1995).
With faster computers and more reliable software, computer simulation is becoming
an important tool in orthopaedic research. Future research programmes will use
computer simulation to reduce the reliance on animal experimentation, and to
complement clinical trials (Prendergast 1997).
1.1
Aims and Objectives
Cementless hip stems are widely used and gaining popularity over its cemented
counterpart, but the major concern is their stability. Analysing factors that could
compromise the stability is crucial to its success, and the valuable information
obtained from these analyses could be used to improve the stability and therefore
improve the confidence of patients and surgeons alike. This study will concentrate on
issues surrounding the stability of cementless hip stems using finite element analyses.
6
It is hoped that this study will provide quantitative and qualitative data to help both
surgeons and engineers on issues related to the stability of cementless hip stems, in
order to improve its short-term and long-term successes.
7
Chapter 2
Technical Paper Published
1
Conclusions and Recommendations
Cementless hip stems are gaining popularity in hip joint arthroplasty but the issues
related to their stability are a major concern.
This research uses Finite Element
Analyses to study various factors that could affect the stability of cementless hip stems.
The effect of muscle forces affecting the FE predictions was analysed. Muscle forces
should be included in all FE analyses because ignoring them will underestimate the
magnitude of micromotion and the surface area unfeasible for bone growth. Another FE
parameter studied was the bone material properties. The bone’s elastic modulus was
gradually reduced to simulate weaker bone mass. The results showed that as the
modulus was reduced, the interface micromotion increased.
This project has achieved its objective of simulating failure of cementless hip
prostheses. However, there are many areas where further improvements could be made.
The analyses were conducted on a standard commercially available finite element
package. As such, the results that can be shown are limited to those available within the
8
package. An algorithm tailored to study the micromotion of bone-implant interface
would be further analysed. With such a code, there are many aspects of replacement
surgery that could be analysed, which includes:
•
The effect of surface roughness of cementless stems.
•
The effect of the overall geometry.
•
The effect of proximal vs distal fixation concept.
•
The effect of surgical error such as misalignment.
•
The effect of macrofeatures.
•
The effect of bone pathology.
9
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the Interface Membrane of Failed Isoelastic Cementless Prostheses", International
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Dorr, L. D., Wan, Z. N., & Gruen, T. 1997, "Functional results in total hip replacement in
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Duffy, G. P., Berry, D. J., Rowland, C., & Cabanela, M. E. 2001, "Primary uncemented
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Duffy, G. P., Muratoglu, O. K., Biggs, S. A., Larson, S. L., Lozynsky, A. J., & Harris, W.
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implant design", Clinical Biomechanics, vol. 12, no. 6, pp. 343-366.
Rasquinha, V. J., Dua, V., Rodriguez, J. A., & Ranawat, C. S. 2003, "Fifteen-year
survivorship of a collarless, cemented, normalized femoral stem in primary hybrid total
hip arthroplasty with a modified third-generation cement technique", Journal of
Arthroplasty, vol. 18, no. 7, pp. 86-94.
Simmons, C. A., Valiquette, N., & Pilliar, R. M. 1999, "Osseointegration of sintered
porous-surfaced and plasma spray- coated implants: An animal model study of early
postimplantation healing response and mechanical stability", Journal of Biomedical
Materials Research, vol. 47, no. 2, pp. 127-138.
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